Method and apparatus for printing on a flat substrate

ABSTRACT

The invention concerns an assembly for printing on a substrate having a camera for recording a reference pattern; a computer connected to the camera to store and modify, if required, data (N) concerning the reference pattern; and a printer whereof at least the print head is controlled by a printer file (FI) generated by the computer. The invention is characterised in that it includes a system for supporting and moving the substrate; for analysing and comparing a pre-recorded pattern with a pattern located on the substrate, and for adapting or not the data (N) concerning the reference pattern as a result of the comparison; and for generating a printer file (FI) based on the data whether or not modified.

The present invention relates to the general technical field of printingon a flat substrate, for example a fabric, by reference to which thepresent invention will be introduced, discussed and exemplified.

By “fabric” is meant generically any woven or nonwoven cloth.

The invention is concerned more particularly with printing on a fabricof the “jacquard” type. Such printing must make it possible to print animage, a design or colors on a figured pattern pre-existing in thefabric.

In all the description and the claims below, the term “pattern” in thesingular designates a unitary or single pattern or one which is repeatedin at least one direction or dimension of the flat substrate, forexample of the fabric, and a set of patterns identical or different fromone another.

Patterns of the “jacquard” type are produced by different ways ofinterlacing the threads, thus giving said patterns their form, theircontour and a surface or textured appearance, with some contrast. Thepatterns are therefore figured directly in the fabric.

Traditional printing, known as “flat-screen” printing, is defined asbeing printing in which a printing screen is used. The latter has acutout according to the form of a pattern.

A mask is a band of greater or lesser length which is arranged on thefabric and is provided with cut-out patterns.

Printing known as “double-stencil” printing is defined as being printingin which a printing screen is superposed on a mask, in order to carryout screen printing.

Printing methods are known which involve accurately fastening a fabricto a table and manufacturing very expensive printing screens which arearranged successively on the fabric, so as to produce prints throughsaid screens in a way in register with the figured patterns of thefabric. Such a method requires considerable human resources in order toposition the fabric and/or the printing screens. The fastening of thefabric to a table is a very time-consuming manual operation.

Such a method assumes the use of fixed-form screens which do not make itpossible to obtain high accuracy. An accuracy of the order of acentimeter is obtained, which may represent an appreciable offset duringprinting.

It is also known, from the document DE 3 917 957, to employ a method forprinting a fabric with designs and/or colors, which involves:

-   -   pre-recording a pattern with the aid of a camera or computer;    -   where appropriate, processing the pre-recorded pattern;    -   and generating a printing file comprising data relating to the        pre-recorded and/or processed pattern, so as to control the        printing from a printer connected to the computer. The fabric is        thus printed with the patterns pre-recorded in the computer, for        example repetitively.

This method does not make it possible to identify and recognize apre-existing pattern in the fabric.

Moreover, such a method, by its very conception, is independent of thestructure of the fabric and, more specifically, of any distortion of thepattern figured in the fabric. There is no provision for adapting to thepattern figured in the fabric.

The document EP 0 795 400 relates to a printing method for printing asubstrate, in this particular case paper. This method involvespre-recording at least one pattern numerically, generating a printingfile comprising data relating to the pre-recorded pattern and carryingout printing generated directly or indirectly from the printing file.

Reference patterns are recognized, using a shade separation technique.This technique is implemented by successively generating elementaryimages corresponding to shades or to superpositions of particularshades. The elementary images, obtained by means of screens, cylindersor printing presses, are positioned in relation to one another in orderto come as closely as possible to the pre-recorded reference patterns.

The various shades, applied in successive layers, are thereforerepositioned in relation to one another in order to obtain the finalimage. Moreover, repositioning is controlled by means of a comparisonbetween a reference image and the actual printed image resulting from aprinting test.

For processing purposes, this method allows only a relative displacementbetween fixed or unchangeable images.

The method is implemented in a printing technique, not by the continuousprinting of a fabric, on which it is necessary to identify, analyze andprocess a pattern integrated into the substrate, said pattern notnecessarily being repeated identically in its form and/or its positionon the substrate.

This method does not make it possible to modify the geometry of apattern substantially in the measurement or the paper printing pressused does not make it possible to set the relative positioning ofelementary shades.

The essential object of the present invention is a method making itpossible to print any pattern on a flat substrate, for example a fabric,in a recorded or identified manner with respect to any pre-existingpattern on said fabric, and, in particular, any figured pattern.

According to the invention, the printing method involves:

-   -   continuously or discontinuously identifying at least one pattern        of a fabric by relative displacement between said fabric and an        image acquisition means;    -   comparing the identified pattern in real time with a reference        pattern pre-recorded for recognition purposes;    -   adapting the pre-recorded reference pattern in line, in order to        superpose it on and/or fit it to the identified pattern, and        generating a printing file;    -   and carrying out printing dot by dot, directly or indirectly,        according to the printing file.

The objects assigned to the present invention are also achieved with theaid of a “computer program” product loadable directly into the internalmemory of a computer and comprising software code portions for executingthe steps of the method described below, when said program is executedon a computer.

The present invention also relates to an assembly for printing on asubstrate, comprising:

-   -   a camera for recording a reference pattern;    -   a computer connected to said camera, in order to store and,        where appropriate, modify data relating to the reference        pattern;    -   and a printer, of which at least one head for printing dot by        dot is controlled by a printing file generated by the computer.

According to invention, the printing assembly comprises:

-   -   a means for the support and movement of the substrate;    -   analysis means in order, on the one hand, to compare a        pre-recorded reference pattern in real time with a pattern        identified on the substrate, and, on the other hand, to adapt or        not the data relating to the reference pattern as a function of        the result of the comparison;    -   and means for generating a printing file from the data modified        or not.

The method according to the present invention has the advantage ofmaking it possible to print fabrics for which it is not possible torecognize by transparency patterns which are figured in said fabric.

Another advantage is linked to the automation of the printing operationsand, in particular, the identification of the patterns figured in thefabric.

This automation also relates to the printing operation per se which maybe carried out directly from pre-recorded instructions. The printingmethod according to the invention makes it possible to carry outdetailed work automatically, in line, on the form of the images to beprinted, in order to obtain an accurate register with respect to theform and position of the pre-existing pattern of the fabric.

Such a pattern may be defined, in particular, in relation to the edgesof the fabric.

Another advantage of the method according to the invention is thepossibility of combining some steps with traditional printing, forexample using printing screens. In fact, such a combination makes itpossible to obtain special interesting esthetic effects.

Continuous adaptation to the patterns figured in the fabric makes itpossible to take into account, on the one hand, the actual positioningsof said patterns and, on the other hand, possible deformations ordistortions of said patterns attributable, for example, to manufacturingdefects or to mounting faults on the means for the movement of thefabric. The fabric may, for example, be locally tensioned to a greateror lesser extent in relation to the movement members, thus generating anoffset or a deformation of one or more patterns.

Another unexpected advantage of the method according to the invention isthat it is free of the limitations imposed by a pre-recorded andunchangeable reference model or pattern.

In fact, this reference pattern may, according to the invention, beprocessed or adapted in such a way as to be identified as closely aspossible with the actual pattern read and recognized on the fabric. Incontrast to screen printing and cylinder printing, the image to beprinted is thus constructed completely or partially as the fabric movespast in front of the camera. During this construction, the pre-recordedpattern is used, which is converted by displacement and/or deformationso as to be superposed on the actual pattern figured in the fabric.

According to the invention, preferably, the fabric is moved in relationto an identification means and to a printing means at a speed compatiblewith the identification speed and the printing speed.

According to the invention, preferably, printing is adapted in line bymeans of the virtually instantaneous recognition of differentpre-existing patterns capable of succeeding one another or alternatingwith one another on the fabric.

The method according to the invention makes it possible to printpatterns in situations where traditional screen or cylinder printingdoes not afford sufficient accuracy with respect to a pre-existingpattern on the fabric.

As an example, even if the fabric is tensioned so as to deform thepatterns which are figured on it (jacquard fabric), these deformedpatterns are recognized and accurately overprinted. When the fabric issubsequently relaxed, the figured patterns resume their initial formwhich will remain correctly printed. There will be no offset between thefigured patterns and the printed patterns corresponding to all thereference patterns.

Other characteristics and advantages will be gathered from a reading ofthe detailed description given below by way of non limiting example,with reference to the drawings in which:

FIG. 1 shows a flow chart of the steps of the method according to theinvention;

FIG. 2 shows diagrammatically an example of printing equipment or aprinting installation according to the invention;

FIGS. 3 to 12 show examples of printing by the method according to theinvention.

FIG. 1 shows a diagrammatic flow chart of the steps of the methodaccording to the invention.

According to this method, one or more patterns are recorded with the aidof an image acquisition means of the camera type, connected to acomputer. The computer, with the aid of a suitable program, thereforemakes it possible to acquire 100 a reference pattern in numerical formby image recognition and to record 101 the corresponding data N. Thesedata N subsequently allow the computer to generate 102 a reference gridT comprising characteristic dots defining the geometry of the referencepattern. The reference image IR corresponding to the grid (T) isrecorded 103. The latter may advantageously be displayed on a screen.Steps 101 to 103 above correspond to a learning phase (A) in respect ofthe reference pattern.

In the method according to the invention, one or more patterns aresubsequently identified in a fabric, and also their position, with theaid of a camera connected to the computer, so as to identify by imagerecognition a set of actual characteristic dots for each pattern, andthereby to generate 201 an actual grid (R) of actual characteristicdots.

This actual grid (R) constitutes the actual architecture of the patternor patterns of the fabric. These steps 200 and 201 thus represent anidentification phase (B) in respect of each pattern by the methodaccording to the invention.

The latter also comprises a comparison and adaption phase (C), in whichthe identified patterns are compared with the reference patterns forrecognition purposes.

Once the identified pattern has been recognized, the reference patternis adapted by means of the computer so as to superpose it on theidentified pattern. These steps involve, on the one hand, comparing 300the actual grid (R) with the reference grid (T), so as to determine thedistance between each reference characteristic dot and eachcorresponding actual characteristic dot.

According to the method, an adaptation 301 of the reference grid (T) issubsequently carried out, by said reference grid (T) being deformedand/or centered in order to superpose it on the actual grid (R) of thefabric.

What is known as the deformation method involves taking as a referencethe actual grid of the fabric and positioning the print in relation tothe actual position of a figured pattern on the moving fabric.

By “figured pattern” is meant any design, decoration or inscription,colored or not, obtained in an integrated manner in the fabric, forexample during weaving, or obtained in an applied manner, for example byprinting according to any technique suitable for a textile piece.

The method of deformation processing involves, for example, deformingthe reference grid (T) by a second-order interpolation. The programloaded in the computer and comprising instructions for recalculating theposition of the characteristic dots defining the reference grid is knownper se.

What is known as the method of processing by centering involves takingas an identified pattern the edges of the moving fabric and positioningthe print in relation to said edges. This method may be considered as asimplified deformation method.

Another processing method may involve a combination of the centeringmethod and of the deformation method for the reference grid (T). Theadaptation of the reference grid (T) thus corresponds to a method ofprocessing by the centering and/or the deformation of the reference grid(T).

What is known as a combined processing method involves, for example,dividing a printing zone of the fabric into a plurality of parts towhich the operator assigns a processing method. Some parts of thereference image (IR) can thus be centered, while other parts of thissame reference image (IR) may be deformed.

To obtain particular esthetic effects, it is advantageous to prefer oneor other of these three processing methods.

After the comparison step 300 in respect of the grids (R) and (T) and,if appropriate, the adaptation step 301 in respect of the reference grid(T), a superposition of the actual grid (R) and of the reference grid(T) is obtained. This superposition makes it possible to pass to aprinting phase (D), in which a printing file (FI) is generated 400 inpixels from the reference grid (T) adapted or not.

This printing file (FI) subsequently makes it possible to control 401 aprinting head of the printer and consequently to position said printinghead on the fabric.

This printing phase (D) may, where appropriate, also be obtained withoutthe adaptation of the reference grid (T), when the reference grid (T)and the actual grid (R) are already superposed during the comparisonstep in respect of the grids (R) and (T).

The printing file (FI) comprises, where appropriate, data relating to amethod for processing by centering, to a method of processing bydeformation or to a combination of said methods.

According to the invention, the printing method involves dividing theimage to be printed into different zones, assigning a processing methodto each zone and hierarchizing the printing of the various zones, so asto print said zones in a defined order, this generally being carried outin one printing operation.

The printing method makes it possible, for example, to apply andsuperpose different layers of coloration on the same fabric portion.This portion comprises, for example, a partial overlap of printing zoneswhich are assigned respectively different processing methods.

The order or relative priority of the printing of such zones isdetermined and calculated as a function of the desired final result, forexample of the desired esthetic effect and, if appropriate, of theadaptation operation or operations which have been undertaken. Printingmay take account, for example, of a special form and/or a superpositionof different colorations. When there is superposition, it is the lastprinting layer which predominates and conceals the other layers.

According to the invention, printing is obtained by ink jet.

According to the invention, the method also involves recalculating thecolor of the pixels of the printing file by means of the computer,starting from the recorded pixels of the reference pattern, and takinginto account the method of adaptation of the reference grid. Themodification in the position of the characteristic reference dots inorder to allow for the change in form of the figured pattern in relationto the reference pattern likewise takes the form of a new calculation ofeach pixel. It is thus possible to reconstruct an image which isfaithful to the reference pattern but the form of which takes account ofthat of the figured pattern.

This step likewise corresponds to a complementary adaptation 500 of thereference grid (T), said adaptation being indicated diagrammatically inFIG. 1 and being appropriate to implement after the comparison andadaption phase (C).

The invention also relates to a “computer program” product loadabledirectly into an internal memory of a computer. This “computer program”product thus comprises software code portions for executing the steps ofthe method according to the invention, described above with reference toFIG. 1, when said program is executed on a computer (not shown).

FIG. 2 shows diagrammatically an exemplary embodiment of a printingassembly or printing equipment for carrying out the printing methodaccording to the invention. The printing assembly comprises a supportand movement means 3 making it possible to support and move the fabric2. This means is known per se. The printing assembly comprises a camera4 for identifying the patterns figured on the fabric 2. A lightingdevice 6 is also provided. The direction of movement of the fabric 2 isindicated diagrammatically by the arrow (F).

A computer, the internal memory of which is loaded with a program makingit possible to execute the steps of the method described with referenceto FIG. 1, is identified in FIG. 2 under the reference 50.

The computer 50 is connected to the camera 4 and stores and modifies,where appropriate, and as above, the data N relating to the referencepattern, and the printer 81 comprises at least one head 8 for printingdot by dot, controlled by a printing file (FI) generated by the computer50.

According to one embodiment, the printing assembly comprises a codingmeans 10 connected to the computer 50 and making it possible to identifyand measure the advance of the fabric on its support and to trigger theacquisition of the figured patterns by the camera 4.

The printing assembly operates, for example, by printing successivestrips on the fabric 2 moving past at defined rates of advance. Theacquisition of data relating to the identification (recognition andposition) of the figured patterns by the camera 4 likewise, in thiscase, takes place according to such rates of advance.

Thus, the fabric 2 advances at a defined rate orthogonally to thedirection of displacement of a printing head. This movement of thefabric 2 is subsequently interrupted for the time necessary for printinga corresponding strip of the fabric 2.

The camera 4 is associated with the lighting device 6 consisting, forexample, of light-emitting diodes or of high-frequency neon lights. Thelighting is preferably glancing in relation to the fabric 2, in order toemphasize more the contrast of the figured patterns in relation to therest of the fabric.

The computer program controlling the printing method recognizes thevariations in contrast in order to determine the form or contour of anidentified figured pattern, this being for purposes of recognition amongthe pre-recorded reference patterns. The program therefore searches forthe characteristic dots of the figured pattern by means of aconventional form recognition method. The latter involves identifyingall the forms of a given pattern, the respective centers of gravity ofwhich would be the characteristic dots of said pattern. Numerous formscan be detected, making this identification particularly accurate. Theset of characteristic points of the identified figured pattern thusconstitutes a frame, referred to above as the actual grid.

FIGS. 3 and 4 show an example of the implementation of the printingmethod according to the invention, in which the method of processing apattern by centering is used.

The edges 2 a and 2 b of the fabric 2 are thus identified, and thecentering of a reference pattern 20 in relation to these edges 2 a, 2 bis carried out. The fabric 2 is then obtained, provided with its pattern20 printed in a centered manner (cf. FIG. 4). The data (N) are modifiedonly if the centering of the reference pattern 20 in relation to theedges 2 a, 2 b proves necessary.

FIGS. 5 and 6 show another example of the implementation of the printingmethod according to the invention, in which the method of processing apattern by deformation is used.

By means of the computer, the position of the actual characteristic dots30 is compared in real time with the position of the referencecharacteristic dots 21 of the reference pattern 20. It can thus bechecked whether the actual (R) and reference (T) grids are superposed.In the example of FIG. 5 this is not so, and it can be seen that all thereference characteristic dots 21 projected onto the fabric 2 are notsuperposed on the actual characteristic dots 30.

The computer then determines a new position by a calculation forparticular reference characteristic dots 21, so as to superpose them onthe corresponding actual characteristic dots 30.

The reference grid (T) is thus deformed in real time in order togenerate the printing file (FI).

After this operation, the reference grid (T) and the actual grid (R) aremerged, and a deformed reference image (IR) is provided, which can beprinted with high accuracy onto the figured pattern identified on thefabric 2, as may be seen in FIG. 6.

FIGS. 7 to 9 show an additional example of the implementation of theprinting method according to the invention, in which the combinedprocessing method (centering and deformation) is used, with examples ofthe form of the reference patterns 20 and of figured patterns 2 c in thefabric 2.

The reference pattern 20 consists of a first reference pattern 20 awhich is centered in relation to the edges 2 a, 2 b, without undergoingdeformation. The reference pattern 20 also consists of a secondreference pattern 20 b which is adapted according to deformationprocessing in order to be superposed on the figured patterns 2 c. Thesecond reference pattern 20 b comprises an element 22 which is veryclearly offset in relation to the figured pattern 2 c. This offset isindicated by broken lines in FIG. 8. The adaptation step of the secondreference pattern 20 b consequently makes it possible to deform theelement 22 so that the printing zone which it defines is superposed onthe figured pattern 2 c. Printing is subsequently undertaken on thebasis of the printing file (FI) comprising modified data (N) relating tothe two processing methods. The printed fabric 2 of FIG. 9 is thusobtained.

FIGS. 10, 11 and 12 show by way of example an alternative implementationof the method according to the invention. This method is supplemented inrelation to the example described is FIGS. 7 to 9, in as much as itmakes it possible to hierarchize the printing of various zones.

In fact, the first reference pattern 20 a which is centered in relationto the edges 2 a, 2 b comprises an additional design 23.

The second reference pattern 20 b is adapted by deformation processingaccording to the corresponding description of FIGS. 7 to 9.

According to the invention, the data originating, on the one hand, fromthe recorded reference patterns and, on the other hand, from theidentified figured patterns are taken into account in order to definetwo printing zones corresponding respectively to the first and secondreference patterns 20 a, 20 b.

Hierarchization involves the priority printing of the printing zonecorresponding to the method of centering processing and, subsequently,printing the printing zone corresponding to the method of deformationprocessing.

The element 22 is thus obtained, which is merged with the figuredpattern 2 c which is printed completely and the form of which partiallyconceals the additional design 23. The reference pattern 20 is thereforerestored to the best possible extent, in view of the positioning of thefigured patterns 2 c in the fabric 2.

As an example, the method according to the invention makes it possibleto generate original designs, the graphics of which are closely linkedto the weaving. A printing accuracy of below 0.2 mm is obtained. It ispossible, for example, to print a rider on a horse woven in the fabric2. A perfect register of all the details is obtained. Superposableand/or complementary images are thus obtained, in order to form thefinal pattern on the fabric.

The method according to the invention can employ traditional flat-screenprinting on the basis of the data from the printing file (FI). In thiscase, a control file is generated, capable of controlling a machine forthe manufacture of printing screens or masks.

The printing adopted according to the invention can combine an ink-jetmethod and a traditional method, for example with a flat screen. Theadvantages of the two methods can then be added together in order toobtain novel and original graphic effects.

The printing assembly according to the invention may also be used as asimple device for centering the fabric 2 and advantageously replaceheavy mechanical centering methods.

1. A printing method for printing a flat substrate, for example afabric, involving particularly: pre-recording at least one patternnumerically; where appropriate, processing the pattern thuspre-recorded; generating a printing file (FI) comprising data relatingto the pre-recorded and/or processed pattern and carrying out printinggenerated directly or indirectly from the printing file; continuously ordiscontinuously identifying at least one pattern of a fabric by relativedisplacement between said fabric and an image acquisition means;comparing the identified pattern in real time with the reference patternpre-recorded for recognition purposes; adapting the pre-recordedreference pattern in line, in order to superpose it on and/or fit it tothe identified pattern and generating a printing file (FI); and carryingout printing dot by dot, directly or indirectly, according to theprinting file.